Method and means for detecting the clogging of a grinding wheel or the like

ABSTRACT

The degree of clogging or loading of the working surface of a grinding wheel or the like with the particles of electrically conductive material removed from the work is detected by a detecting coil disposed opposite the working surface of the grinding wheel and fed by a high frequency oscillator circuit so as to produce a magnetic flux such that eddy currents are induced in the conducting particles on the working surface of the grinding wheel. The counterelectromotive force due to the eddy currents causes a corresponding change in the inductance of the detecting coil, so that the frequency of the output signal from the oscillator circuit changes in accordance with the varying inductance of the detecting coil. The resulting output signal is fed through a detecting circuit, an amplifying circuit and an integrating circuit into a comparison circuit which produces an output when the level of the signal supplied from the integrating circuit becomes at least equal to a predetermined threshold.

United States Patent [191 Sata May 7, 1974 v [54] METHOD AND MEANS FOR DETECTING THE CLQGGING OF A GRINDING WHEEL OR THE LIKE [76] Inventor: Toshio Sata, 3-9-11 Shimohoya,

Houya-shi, Tokyo, Japan [22] Filed: Apr. 2, 1973 [.21] Appl. No.: 346,814

Primary Examiner' -Michael J. Lynch Attorney, Agent, or FirmRobert E. Burns; Emmanuel J. Lobato [5 7] ABSTRACT The degree of clogging or loading of the working surface of a grinding wheel or the like with the particles of electrically conductive material removed from the work is detected by a detecting coil disposed opposite the working surface of the grinding wheel and fed by a high frequency oscillator circuit so as to produce a magnetic flux such that eddy currents are induced in the conducting particles on the working surface of the grinding wheel. The counterelectromotive force due to the eddy currents causes a corresponding change in the inductance of the detecting coil, so that the frequency of the output signal from the oscillator circuit changes in accordance with the varying inductance of the detecting coil. The resulting output signal is fed through a detecting circuit, an amplifying circuit and an integrating circuit into a comparison circuit which produces an output when the level of the signal supplied from the integrating circuit becomes at least equal to a predetermined threshold.

8 Claims, 2 Drawing Figures I8 LEVEL serrms l0 'CIRCUIT I1 12 I4 1 I5 17 Z0 osclttnroe nzrecrme mrsemnme COMPARISON y CIRCUIT Cmcuxr cmcun' cmcun Work Detecting Coil Piece I6 y t ER Grinding what 7 FIELD OF INVENTION order automatically to ascertain the most appropriate time for dressing the grinding wheel or the like.

BACKGROUND OF THE INVENTION It is well known that grinding wheels are used for cutting and finishing metal and other materials to the required dimensions. Such grinding wheels are composed of abrasive grains, usually artificial,held together by a bonding -or binding agent. In actual grinding operations, however, the abrasive grains on the working surfaces of the grinding wheels become inevitably clogged with particles of material which has been removed from the work. This clogging of the abrasive grains seriously affects the grinding or cutting quality of the grinding wheels and, moreover, can give rise to surface imperfections in the finished product.

In order to avoid such undesirable effects, the grinding wheels must be dressed or'reconditioned at appropriate time intervals, which usually have been determined on the basis of the number of workpieces ground. However, the optimum moment for dressing the grinding wheels is not ascertainable in this manner, as it is subject to change depending upon the kind of grinding wheel used, the kind of work being ground, the operating conditions, etc.

There has been proposed a method of magnetically detecting the degree of clogging or loading ofa grinding wheel, in which a magnetic head is used to magne-.

tize the particles which have been attached to the working surface of the grinding wheel. Since the degree of magnetization varies in accordance with the amount of particles accumulated on the wheel, the resulting varying degree of magnetization is measured by another magnetic head. However, this method is adoptable only when t he work is iron or other magnetic ma terial but not when it is aluminum, copper, zinc, magnesium or other nonmagnetic material.

As an alternative, there has been proposed a method in which the area occupied by the particles within a given region on the working surfaceof a grinding wheel is measured optically in order to ascertain the degree of clogging or loading. This method has the drawback in that the grinding operation must be discontinued each time the grinding wheel is subjected to the optical measuring operation. Furthermore, since the method utilizes the light reflected by the layer of the particles on the grinding wheel, precise measurement of the degree of clogging or loading is practically impossible in the caseof such glittering particles as those of aluminum and other metals. It is an additional disadvantage of this method that it requires bulky and expensive equipment.

SUMMARY OF THE INVENTION In view of the foregoing disadvantages of the prior art, it is an object of the present invention to provide a novel and improved method and means for detecting the degree of clogging or loading of a grinding wheel or the like with particles removed from the work being ground, so that the most appropriate moment for dress ing the grinding wheel or the like is ascertainable automatically to improve the accuracy and efficiency of the grinding operation.

Another object of the invention is to provide a method and means of infallibly detecting the degree of clogging or loading of a grinding wheel or the like without being influenced'by the presence of liquid coolant, light, or other extraneous matters or phenomena.

A further object of the invention is to provide a method and means capableof accurately detecting the degree of loading or clogging of a grinding wheel or the like with the particles removed from the work being ground thereby, whetherthe work is of magnetic or nonmagnetic material, provided that it is electrically conducting.

According to the method of this invention, an alternating current of selected high frequency is delivered to a detecting or inspecting element such as a coil positioned opposite the working surface of a rotary grind ing member such asa grinding wheel, and a resulting magnetic flux generated by the detecting element is applied to the layer of the conducting particles on the working surface of the rotary grin-ding member to induce eddy currents therein. The counterelectromotive force due to the eddy currents produces a corresponding change in the inductance of the detecting element and this in turn results in varying the frequency of the output signal of the'oscillator circuit. This variable frequency output signal is converted into pulses of corresponding variable amplitude which are amplified and fed into an integrating circuit which integrates the pulses arriving during each of successive predeter mined periodsof time. The output signal from the integrating circuit is fed into a comparison circuit which produces an output when the level of the integrating circuit output signal becomes at least equal to a predetermined threshold. Thus, the output signal from the comparison circuit can be utilized to provide a signal or to actuate a dresser of any suitable construction .to dress the grinding wheel.

The invention together with further objects and advantages thereof, will be more fully understood from the following description of a preferred embodiment taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a schematic block circuit diagram showing a preferred emobdiment of the invention; and

FIGS. 2A, 2B and 2C are graphic representations of waveforms explanatory of the operation of the embodiment of FIG. 1. t

DESCRIPTION OF THE PREFERRED EMBODIMENT In FIG. 1, a grinding wheel 10 is shown grinding a metallic work piece 19. In accordance ith the prior art, the grinding wheel is composed of abrasive grains, such for example as silicon carbide or aluminum oxide, held together by a bonding or binding agent, which may be either a vitrified material or a softer material, such for example as shellac or rubber. A multiplicity of cutting or abrasive grains are exposed on the working surface of this grinding wheel. As successivework pieces are ground, the working surface of the grinding wheel becomes progressively clogged or loaded with metal par ticles removed from the work pieces.

Suitably close to the working surface of the grinding wheel 10 there is disposed an inspecting element in the form of a detecting coil 11 which is connected to an output of an oscillator circuit 12, so that an alternating current produced by the oscillator circuit is delivered to the detecting coil 11. In this particular embodiment of the invention, the output current oscillations of the oscillator circuit 12 are assumed to be in a-high frequency range of from about 1 to megahertz. The current oscillation in the coil 11 produce a magnetic flux which induces eddy currents in metal particles accumulated on the working surface of the grinding wheel 10. The varying counterelectromotive force due to the eddy currents produces a corresponding change in the inductance of the coil 11. Although the oscillator circuit 12 is a fixed frequency type oscillator, variation in the inductance of the detecting coil 11 causes small variations in the output frequency of the oscillator circuit by mutual inductance. Thus, the output frequency of the oscillator is varied according to the accumulation of metal particles on the working surface of the grinding wheel 10.

The oscillator circuit 12 is further connected to a detecting circuit 13 which comprises a frequency-voltage transducer for converting frequency changes to voltage changes. The output of the detecting circuit 13 is connected to the input of an amplifying circuit 14, and the output of this amplifying circuit 14 is connected to an input of an integrating'circuit 15. The integrating cir- 'cuit 15 has another input through which an output signal comprising spaced timing pulses is supplied from a timer 16. Thus, the integrating circuit 15 will integrate, in a known manner, the output signal from the amplifying circuit 14 during a period between successive output pulses from the timer 16.

The pulses produced by the timer 16 may be synchronized with the revolving speed of the grinding wheel in such a manner that, for example, the, timer will produce a single pulse with each complete revolution of the grinding wheel. For this purpose a connection between the timer and the grinding wheel may be providedas indicated schematically at 21. However, if desired, the timer 16 may be caused to produce a single pulse with the lapse of each predetermined length of time.

The output of the integrating circuit is connected to one of the inputs of a comparison circuit 17, to the other input of which is connected the output of an adjustable level setting circuit 18. In the comparison circuit 17, therefore, the level of the output signal from the integrating circuit 15 is compared with a threshold level determined by the level setting circuit 18. Only when the output signal level from the integrating circuit 15 is equal to or higher than the threshold level, the comparison circuit 17 will produce an output signal at the output terminal 20 which may be used as desired, for example to actuate a signal or to initiate the operation of a dresser of any suitable type for dressing the working surface of the grinding wheel.

In the preferred embodiment of this invention, with its various components arranged substantially as hereinbefore described, the grinding wheel 10 is caused to rotate at a surface speed of, for example, about to 60 meters per second and is fed against the work 19, with a traversing movement if desired, to grind the work to the required dimensions. As mate'rialis gradually removed from the work by this grinding operation, the abrasive grains on the working surface of the grinding wheel become inevitably clogged with the particles of material removed from the work.

Since an alternating current with a frequency of from about 1 to 5 megahertz is being delivered to the detecting coil 11 from the oscillator circuit 12, the detecting coil produces a varying magnetic flux. Due to the variation in this magnetic flux caused by the conducting.

layer of electrically conductive particles on the working surface of the rotating grinding wheel 10, eddy currents are induced in the conductive layer. The counterelectromotive force produced by the eddy currents, in turn causes corresponding changes in the inductance of the detecting coil 11. By reason of mutual inductance, the frequency of the output signal from the oscillator circuit 12 changes in accordance with the varying inductance of the detecting coil and hence in accordance with the accumulation of conducting particles on the grinding wheel. As the grinding wheel is in constant rotation, the frequency of the output signal of the oscillator circuit 12 is subject to rapid short term variation by reason of uneven distribution of conductive particles around the periphery of the grinding wheel and is also subject to progressive long term variation by reason of the progressive accretion of conductive particles on the working surface of the grinding wheel.

The output signal with its changing frequency from the oscillator circuit 12 is delivered to the detecting circuit 13 and hence to the amplifying circuit 14. The detecting circuit 13 converts the FM input (frequency changes) to an AM output (voltage changes). As the clogging of the working surface of the grinding wheel is ordinarily not uniform but occurs discontinuously as discrete particles or patches distributed at random around the periphery of the grinding wheel, the output signal of the detecting circuit 13 appears as a train of pulses the amplitude of which corresponds to the size of the respective particle of patch. The output of the detecting circuit 13 is amplified by the amplifying circuit 14 and appears as a train of pulses of random spacing and varying amplitude as shown schematically in FIG. 2A. The values of these pulses P, through P, vary in substantial accordance with the thickness or amount of the conducting particles which have accumulated on the corresponding portion of the working surface of the grinding wheel 10. The pulses having high peak values, therefore, indicate the accumulation of a corresponding amount of the conducting particles on the grinding wheel. It will be understood that FIG. 2A is schematic and does not purport to show all the pulses that occur in one revolution of the grinding wheel.

The amplifying circuit 14 delivers the train of pulses P to P to one of the inputs of the integrating circuit 15. It will be noted, however, that the introduction of these pulses into the integrating circuit 15 takes place simultaneously with the delivery of spaced timing pulses T T etc., FIG. 28, to the other input of the integrating circuit from the timer 16. The integration of the pulses P, to P,, by the integrating circuit 15 proceeds for a predetermined length of time 1, from pulse T, until the next pulse T is delivered from the timer 16 to the integrating circuit 15. Thus, as shown in FIG. 2C,

the integrating circuit produces an output signal at the end of each predetermined length of time t.

This output signal from the integrating circuit is delivered to one of the inputs of the comparison circuit 17, where its level is compared with the threshold level which has been determined by the level setting circuit 18. In case the level of the output signal from the integrating circuit is equal to or higher than the threshold level, the comparison circuit produces its output, which can be used as desired, for example for actuating an audible or visual signal or for actuating the dresser of any suitable construction. During the subsequent dressing operation of the grinding wheel 10, the grinding operation of the work 19 may have to be suspended.

If, on the other hand, the level of the aforesaid output signal from the integrating circuit 15 is lower than the threshold level determined by the level setting circuit 18, the comparison circuit 17 produces no actuating signal so that the grinding operation of the work 19 proceeds without interruption. It is of course understood that, in the meantime, the amount of the conducting particles which have been attached to the working surface of the grinding wheel 10 is being detected continuously by the detecting coil 11, and that the above described procedure of operation involving this detecting coil 11 through the comparison circuit 17 is taking place continuously. If desired a meter is also connected to the output of the integrating circuit so that the progressive accretion of conductive particles on the grinding wheel can be continuously observed. By use of a recording meter, the clogging characteristics of the grinding wheel under given operating conditions can readily be determined.

In this manner, the presence of the slightest amount of the conducting particles on the working surface of the grinding wheel can be detected to permit the grinding wheel to be dressed at the most. appropriate moment. Assuming for instance that the current delivered from the oscillator circuit 12 to the detecting coil 11 has a frequency of about 5 megahertz, and that the grinding wheel 10 has a diameter'of 300 millimeters and is rotated at the rate of 1,800 revolutions per minute, then the invention will exhibit its full detecting ability if there are more than 2,000 regions of the conducting particles spaced apart from each other by the abrasive grains on the working surface of the grinding wheel.

Although the present invention has been shown and described hereinbefore in terms of a preferred embodiment, it is to be clearly understood that all matter described herein or shown in the accompanying drawings is by way of example only and is not intended to impose limitations on the invention. For example, it will be apparent that the invention is applicable not only to grinding wheels as in the foregoing embodiment but to abrasive belts or similar rotary grinding members as well. It is therefore appropriate thatthe invention be construed broadly and in a manner consistent with the proper scope of the appended claims.

What I claim and desire to secure by letters patent is:

1. In a method of continuously detecting the degree of clogging of the working surface of a rotary grinding member with particles of electrically conducting mate rial removed from the work being ground, the steps of: supplying an alternating current of selected high frequency to an inspecting element having the characteristics of generating an alternating flux field and having a variable reactance, positioning said inspecting element close to the working surface of said rotary grinding element while the latter is rotating to apply said flux field to particles of electrically conducting material lodged on said working surface and thereby produce counterelectromotive force which varies the reactance of said inspecting element, said counterelectromotive force and hence the reactance of saidinspecting element varying with the incremental quantities of said conducting material distributed at random on the periphery of said grinding member, continuously detecting the reactance of said inspecting element to produce a train of signals corresponding in amplitude to the varying reactance of said inspecting element and hence to the quantities of conductive material on the working surface of said grinding member, integrating said sig nals during each successive periods of uniform selected length, and comparing the integrated signal to a selected standard to produce an output signalwhen the integrated signal at least equals said standard.

2. A method according to claim 1, in which said inspecting element supplied with said alternating current generates a magnetic flux which induces eddy currents in electrically conducting material particles on the working surface of said grinding member, the counterelectromotive force due tosaid eddy currents producing a corresponding change in the inductance of said inspecting element.

3. A method according to claim 2, in which variation in the inductance of said inspecting element produces corresponding variation of the frequency of said alternating current, the inductive reactance of said inspecting element being detected by detecting the resultant frequency of said alternating current.

4. A system for continuously detecting the degree of clogging of the working surface of a rotary grinding member with particles of electrically conducting material removed from the work being ground, comprising:

an inspecting element positioned close to the working surface of said grinding member,

an oscillator circuit supplying alternating current of selected high frequency to said inspecting element, said inspecting element comprising means for generating a magnetic flux when supplied with alternating current from said oscillator circuit and thereby inducing eddy currents in particles of conducting material on the working surface of said rotary grinding member as they pass said inspecting element,

said eddy currents producing a counterelectromotive force to vary the inductance of said inspecting element in accordance with incremental quantities of said conductive material distributed at random around the periphery of said grinding member,

circuit means for continuously detecting the reactance of said inspecting element and producing a train of signals corresponding in amplitude to the varying reactance of said inspecting element and hence to the quantities of conductive material on the working surface of said grinding member,

circuit means for integrating said signals during each of successive periods of time,

timing means connected with said integrating circuit means and supplying timing signals to said integrating circuit means to define said successive time periods,

comparison circuit means for comparing the level of integrated signals received from said integrating circuit means with a selected standard and producing an output signal when said integrated signal at least equals said standard, and circuit means for supplying said standard to said comparison circuit means. 5. A system according to claim 4, in which said inspecting element comprises a coil the inductance of which is varied by the counterelectromotive force produced by eddy currents generated in said particles of conductive material on the working surface of said grinding member, and which is connected with said oscillating circuit in such manner that variation of inductance of said coil varies the output frequency of said ostion of said grinding member. 

1. In a method of continuously detecting the degree of clogging of the working surface of a rotary grinding member with particles of electrically conducting material removed from the work being ground, the steps of: supplying an alternating current of selected high frequency to an inspecting element having the characteristics of generating an alternating flux field and having a variable reactance, positioning said inspecting element close to the working surface of said rotary grinding element while the latter is rotating to apply said flux field to particles of electrically conducting material lodged on said working surface and thereby produce counterelectromotive force which varies the reactance of said inspecting element, said counterelectromotive force and hence the reactance of said inspecting element varying with the incremental quantities of said conducting material distributed at random on the periphery of said grinding member, continuously detecting the reactance of said inspecting element to produce a train of signals corresponding in amplitude to the varying reactance of said inspecting element and hence to the quantities of conductive material on the working surface of said grinding member, integrating said signals during each successive periods of uniform selected length, and comparing the integrated signal to a selected standard to produce an output signal when the integrated signal at least equals said standard.
 2. A method according to claim 1, in which said inspecting element supplied with said alternating current generates a magnetic flux which induces eddy currents in electrically conducting material particles on the working surface of said grinding member, the counterelectromotive force due to said eddy currents producing a corresponding cHange in the inductance of said inspecting element.
 3. A method according to claim 2, in which variation in the inductance of said inspecting element produces corresponding variation of the frequency of said alternating current, the inductive reactance of said inspecting element being detected by detecting the resultant frequency of said alternating current.
 4. A system for continuously detecting the degree of clogging of the working surface of a rotary grinding member with particles of electrically conducting material removed from the work being ground, comprising: an inspecting element positioned close to the working surface of said grinding member, an oscillator circuit supplying alternating current of selected high frequency to said inspecting element, said inspecting element comprising means for generating a magnetic flux when supplied with alternating current from said oscillator circuit and thereby inducing eddy currents in particles of conducting material on the working surface of said rotary grinding member as they pass said inspecting element, said eddy currents producing a counterelectromotive force to vary the inductance of said inspecting element in accordance with incremental quantities of said conductive material distributed at random around the periphery of said grinding member, circuit means for continuously detecting the reactance of said inspecting element and producing a train of signals corresponding in amplitude to the varying reactance of said inspecting element and hence to the quantities of conductive material on the working surface of said grinding member, circuit means for integrating said signals during each of successive periods of time, timing means connected with said integrating circuit means and supplying timing signals to said integrating circuit means to define said successive time periods, comparison circuit means for comparing the level of integrated signals received from said integrating circuit means with a selected standard and producing an output signal when said integrated signal at least equals said standard, and circuit means for supplying said standard to said comparison circuit means.
 5. A system according to claim 4, in which said inspecting element comprises a coil the inductance of which is varied by the counterelectromotive force produced by eddy currents generated in said particles of conductive material on the working surface of said grinding member, and which is connected with said oscillating circuit in such manner that variation of inductance of said coil varies the output frequency of said oscillator circuit.
 6. A system according to claim 5, in which said detecting circuit means comprises means for detecting variation in frequency of the output frequency of said oscillator circuit.
 7. A system according to claim 4, further comprising amplifying circuit means connected between said detecting circuit means and said integrating circuit means to amplify the output of said detecting circuit means.
 8. A system according to claim 4, comprising means interconnecting said timing means with said grinding member to synchronize said time periods with the rotation of said grinding member. 